Printed wiring board and method for manufacturing the same

ABSTRACT

In a printed wiring board, an odd number (n) of conductive layers ( 11 - 13 ) and insulating layers ( 21 - 23 ) are alternately laminated upon each other. The first conductive layer ( 11 ) is a parts connecting layer and the n-th conductive layer ( 13 ) is an external connecting layer which is connected to external connecting terminals ( 7 ). The second to (n−1)-th conductive layers ( 12 ) are current transmitting layers for transmitting internal currents. The surface of the n-th insulating layer ( 23 ) in a state where the external connecting terminals ( 7 ) are exposed on the surface. It is preferable to make the initial insulating layers of a glass-cloth reinforced prepreg and the external insulating layers of a resin.

BACKGROUND OF THE INVENTION

The present invention relates generally to a multilayered printed wiringboard capable of realizing high-density packaging and a method formanufacturing the same, and particularly to a printed wiring boardhaving an odd number of conductive layers, a printed wiring board havingbuild-up layers formed by using the additive method and the like, amethod of forming interconnecting through holes for electricallyconnecting conductive layers and narrowing the pitch between solderballs for external connection and the interconnecting through holes.

Conventional printed wiring boards include those having conductivelayers 911 to 914 built up successively, as shown in FIG. 42. Theconductive layers 911 to 914 are electrically connected to one anothervia interconnecting through holes 931 to 933. Insulating layers 921 to923 are interposed between the conductive layers 911 to 914,respectively.

The conductive layer 911 is a component-connecting layer on which anelectronic component 961 is mounted and conducts electric currents inand out of the electronic component 961. The conductive layer 911 whichis one of the outermost layers and the electronic component 931 areelectrically connected to each other by bonding wires 962. Theconductive layer 914 which is the other outermost layer serves as anexternal connecting layer for connecting external connecting terminals97 and leading electric currents in and out of a printed wiring board941. The internal conductive layers 912 and 913 are electric currenttransmitting layers for transmitting internal currents of the printedwiring board 941.

Next, the method of manufacturing the above printed wiring board will bedescribed.

First, as shown in FIG. 43, conductive layers 912 and 913 are formed onthe upper side and lower side of an insulating layer 922 respectively.Further, interconnecting through holes 932 are formed through theinsulating layer 922, and the wall of each interconnecting through hole932 is covered with a metal plating film 95. A resin 92 is then packedin the interconnecting through holes 932.

Next, an insulating layer 921 and a copper foil are laminated on theupper side of the insulating layer 922, while an insulating layer 923and a copper foil are laminated on the lower side, followed by etchingof the copper foils to form conductive layers 911 and 914.

Subsequently, as shown in FIG. 44, interconnecting through holes 931 and933 are formed through the insulating layers 921 and 923 to expose thesurfaces of the internal conductive layers 912 and 913, respectively.

Then, as shown in FIG. 42, a metal plating film 95 is formed on thewalls of the interconnecting through holes 931 and 933, and externalconnecting terminals 97 are bonded onto the surface of the outermostconductive layer 914.

Thus, the printed wiring board 941 can be obtained.

By repeating the procedures shown in FIGS. 43 and 44, the number ofconductive layers to be built up in the printed wiring board 941 can beincreased. The thus obtained printed wiring board has insulating layersand conductive layers built up alternately both on the upper side and onthe lower side of the center insulating layer 922. Therefore, an evennumber of conductive layers are formed according to the above method.

However, the conventional method of manufacturing printed wiring boardsas described above is not suitable for building up an odd number ofconductive layers, although it can build up an even number of conductivelayers efficiently.

To describe, for example, a case where a printed wiring board havingfive conductive layers 910 to 914 built up, as shown in FIG. 45, ismanufactured, the second to fifth conductive layers 911 to 914 are builtup first, as shown in FIG. 46, in the same manner as described above,except that the conductive layer 914 is an unpatterned copper foil.

Next, as shown in FIG. 47, the conductive layer 914 is removedcompletely, and then interconnecting through holes 931 are formed, asshown in FIG. 48, followed by formation of a metal plating film 95 onthe wall of each through hole 931. Subsequently, as shown in FIG. 49,prepregs are laminated and press-bonded to form insulating layers 920and 924. Conductive layers 910 and 941 are then formed on the surfacesof the insulating layers 920 and 924 respectively, followed by formationof interconnecting through holes 930 and 933 through the insulatinglayers 920 and 924 respectively, as shown in FIG. 50. A metal platingfilm 95 is formed on the walls of the through holes 930 and 933, asshown in FIG. 45.

As described above, when a printed wiring board having an odd number ofconductive layers is manufactured, it is necessary, in order to preventwarping of the press-bonded printed wiring board from occurring, tocarry out, after formation of the internal conductive layers 911 and914, the procedure of removing the conductive layer 914. Thus, theconventional method requires wasteful a procedure and is an extremelyinefficient manufacturing method. Further, the insulating layers formedare too thick to meet the purpose of achieving downsizing of printedwiring boards.

Under such circumstances, it can be considered to form an insulatinglayer 920 and a conductive layer 910 only on one side of the insulatinglayer 921. In this case, however, warping of the printed wiring boardcan occur in the step of press-bonding a prepreg for forming theinsulating layer 920.

Meanwhile, in a multilayer build-up type printed wiring board, theinternal insulating layers 921 and 923 to be embedded in it are resins,so that they have high coefficients of water absorption of 0.5 to 1.0%and have high water contents. The water is vaporized naturally withpassage of time to assume the form of water vapor which collects mainly,for example, between the insulating layer 921 and the adjacentinsulating layers 922 and 920 and between the insulating layer 923 andthe adjacent insulating layers 922 and 924.

Accordingly, it is likely that the interlayer adhesion is lowered andthat the layers undergo delamination. Particularly, the greater thenumber of layers laminated, the greater becomes the number ofwater-containing internal insulating layers, and the higher becomes thetendency of interlayer delamination.

Meanwhile, referring to manufacturing of printed wiring boards, there isa method invented by us previously and disclosed in Japanese PatentApplication No. Hei 8-21975. That is, as shown in FIG. 51, a conductivelayer is formed on each insulating layer in step S91, and theninterconnecting through hole-forming through holes are defined in eachinsulating layer in step S92. Steps S91 and S92 are repeatedcorresponding to the number n of insulating layers to be laminated.Next, in step S93, the number n of insulating layers are laminated viaan adhesive material and positioned such that the through holes in therespective layers may communicate with one another to constituteinterconnecting through holes. In step S94, the adhesive material ismelted by heating and the like, and the layers are press-bonded togetherto form a multilayer substrate. In step S95, a conductive material, suchas a solder and the like is packed into the interconnecting throughholes to impart conductivity to them. Thus, a printed wiring board isobtained.

However, in the conventional method of manufacturing printed wiringboards described above, interconnecting through hole-forming throughholes must be defined in each insulating layer independently.Accordingly, the method requires intricate procedures of definingthrough holes. Further, the through holes must be positioned.Particularly, with the reduction in the size of the interconnectingthrough holes, it is becoming difficult to carry out accurateregistration of the through holes.

Meanwhile, in a multilayer printed wiring board, pads for connectingexternal terminals such as solder balls are provided on the outermostlayer. In this case, the interconnecting through holes must beelectrically connected with the pads by connecting circuits. However,the connecting circuits which occupy a large surface area are ahindrance in achieving high-density packaging on the substrate surface.Particularly, in a multilayer printed wiring board, it is necessary toform high-density wiring on the uppermost surface. Further, largeamounts of electric currents must fed in and out through the externalconnecting terminals.

The present invention is directed, in view of the problems inherent inthe prior art described above, to provide a printed wiring board whichcan improve electrical properties of multilayered wiring boards and amethod for manufacturing the same. Particularly, it is a first objectiveof the present invention to build up an odd number of conductive layersefficiently with no warping. A second objective of the present inventionis to prevent delamination of layers. A third objective of the presentinvention is to form interconnecting through holes at accuratepositions. A fourth objective of the present invention is to carry outtransference of a huge amount of electrical information through solderballs for external connection and also to achieve high densification ofsurface packaging.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a printed wiring board havingan odd number n of conductive layers which are built up via insulatinglayers respectively and which are electrically connected to one anotherby interconnecting through holes, characterized in that the firstconductive layer is a component-connecting layer on which an electroniccomponent is to be mounted and which leads electric currents in and outof the electronic component. The n-th conductive layer is an externalconnecting layer for connecting external connecting terminals forleading currents in and out of the printed wiring board. The second to(n−1)-th conductive layers are current transmitting layers fortransmitting internal currents of the printed wiring board, and thesurface of the n-th conductive layer is covered with the n-th andoutermost insulating layer which is the outermost layer with theexternal connecting terminals being exposed.

What is noticeable most in the first aspect of the invention is that theprinted wiring board has an odd number n of conductive layers and thesurface of the n-th conductive layer is covered with the n-th andoutermost insulating layer with the external connecting terminals beingexposed.

In the first aspect of the invention, the odd number n means an integerexcluding 1, which cannot be divided by 2 into a numeral with no decimalfraction, for example, 3, 5 and 7. The reason why 1 is excluded from theodd number n is that such a constitution having only one conductivelayer cannot constitute a printed wiring board.

Actions and effects of the first aspect of the invention will bedescribed.

The printed wiring board according to the first aspect of the inventionhas an odd number n of conductive layers formed between an odd number nof insulating layers respectively. The (n+1)/2-th insulating layer is acentral insulating layer and has on the upper side and lower side thesame number of insulating layers respectively. Accordingly, no warpingoccurs in the printed wiring board during press-bonding of prepregs forforming insulating layers.

Further, conductive layers can be built up on the upper side and lowerside of the central insulating layer efficiently.

Therefore, the printed wiring board according to the first aspect of theinvention is of the structure which facilitates building up of an oddnumber n of conductive layers.

Further, the n-th and last conductive layer is covered with the n-th andoutermost insulating layer serving as the outermost layer. Accordingly,the n-th conductive layer is embedded in the printed wiring board.However, the external connecting terminals connected to the n-thconductive layer are exposed through connecting holes of the n-thinsulating layer, so that electric currents can be led in and out of theprinted wiring board through the external connecting terminals.

The external connecting terminals are preferably solder balls. Thesolder balls can stably lead electric currents in and out through then-th conductive layer.

It is also possible to connect external connecting terminals to thesurface of the n-th conductive layer and to build up an (n+1)-thconductive layer on the surface of the n-th insulating layer present onthe n-th conductive layer. In this case, the resulting printed wiringboard comes to have an even number of conductive layers. Externalconnecting terminals can be connected to the surface of the (n+1)-thconductive layer.

The method of manufacturing the above printed wiring board can beexemplified as follows: a method of manufacturing a printed wiring boardhaving an odd number n of conductive layers which are built up viainsulating layers respectively and are electrically connected to oneanother via interconnecting through holes. The method comprising thesteps of: interposing insulating layers between second to n-thconductive layers respectively and also forming interconnecting throughholes for electrically connecting the conductive layers to one another;laminating a prepreg and a copper foil on the surface of the secondconductive layer, while laminating and press-bonding a prepreg on thesurface of the n-th conductive layer to form a multilayer substratehaving an odd number n of insulating layers and also locating the secondto n-th conductive layers as internal layers of the multilayersubstrate; etching the copper foil to form a first conductive layer;forming interconnecting through holes and connecting holes in the firstinsulting layer and in the n-th insulating layer respectively; forming ametal plating film for electrically connecting the first conductivelayer with the second conductive layer on the walls of theinterconnecting through holes of the first insulating layer; andconnecting external connecting terminals to the surface of the n-thconductive layer exposed through the interconnecting through holes ofthe n-th insulating layer.

What is most noticeable in this method is that a prepreg and a copperfoil for forming the first conductive layer are laminated on the surfaceof the second conductive layer and that only a prepreg is laminated onthe surface of the n-th conductive layer. When the prepregs and thecopper foil are press-bonded, the first insulating layer and the n-thinsulating layer are formed simultaneously by this press-bonding.Accordingly, the second to (n−1)-th insulating layers already laminatedinto a single body receive, on the upper sides and the lower sides,thermal stress evenly from the prepregs during the press-bonding, sothat no warping occurs in the printed wiring board.

Further, the n-th and last conductive layer is covered on the surfacewith an insulating layer formed by laminating and press-bonding aprepreg. In this state, no electric current can be led in and outthrough the n-th conductive layer. However, connecting holes are definedin the outermost insulating layer to expose the external connectingterminals through these connecting holes, and thus electric currents canbe led in and out through the n-th and last conductive layer.

In addition, the external connecting terminals are preferably solderballs. The solder balls can lead stably electric currents in and outthrough the n-th conductive layer.

The conductive layers referred to above mean all sorts of conductivepatterns which can be formed on the surfaces of insulating substrates,for example, wiring circuits, pads, terminals and lands. Conductivepatterns are formed, for example, by etching metal foils or by metalplating.

The insulating layers include synthetic resin single substances,prepregs, etc. The synthetic resins include, for example, epoxy resins,phenol resins, polyimide resins, polybutadiene resins and fluororesins.

Further, the printed wiring board according to the first aspect of theinvention can be utilized, for example, as memory modules, multichipmodules, mother boards, daughter boards and plastic packages.

Methods of defining interconnecting through holes and connecting holesinclude, for example, irradiation of laser beams onto the insulatinglayers at the positions where holes are to be formed; chemical meltingof the insulating layer at the positions where holes are to be formed;and machining using a drill.

A second aspect of the present invention is a printed wiring boardcomprising an internal insulating substrate having a conductor circuitformed on the surface, at least one internal insulating layer laminatedon the surface of the internal insulating substrate, and an externalinsulating layer laminated on the surface of the internal insulatinglayer, the internal insulating layer and the external insulating layerhaving an internal conductor circuit and an external conductor circuitrespectively; wherein the internal insulating layer is of a glasscloth-reinforced prepreg; and the external insulating layer is of aresin.

The glass cloth-reinforced prepreg referred to above means a materialobtained by impregnating a glass cloth base material with a resin.However, in the second aspect of the invention, it is particularlypreferred to use a prepreg containing 30 to 70% by weight of glasscloth. Thus, the coefficient of water absorption can be lowered toprevent interlayer delamination from occurring. Meanwhile, thoseprepregs which contain less than 30% by weight of glass cloth come tohave high coefficient of water absorption to be liable to undergointerlayer delamination, whereas those which contain more than 70% byweight of glass cloth is likely to show low interlayer adhesion, sincethe absolute amount of resin is small.

Further, the outermost insulating layer may be formed using the sameprepreg as used for the internal insulating layers.

It should be noted that in the printed wiring board according to thesecond aspect of the invention, interconnecting through holes, blind viaholes, via holes, etc. can be formed in the internal insulatingsubstrate, internal insulating layer(s) and external insulating layer.Further, on the external insulating layer, lands for mounting solderballs, a solder resist for securing insulation between externalconductor circuits, etc. can be formed. That is, the printed wiringboard according to the second aspect of the invention may have variousstructures generally employed in printed wiring boards.

Actions of the second aspect of the present invention will be describedbelow.

In the printed wiring board according to the second aspect of theinvention, a glass cloth-reinforced prepreg constitutes the internalinsulating layer, while a resin constitutes the external insulatinglayer. That is, since the internal insulating layer contains the glasscloth, coefficient of water absorption can be reduced in the layer.Accordingly, the coefficient of water absorption of the internalinsulating layer as a whole can be reduced.

Therefore, the absolute amount of water to be contained in the internalinsulating layer is reduced, in turn, the absolute amount of water vaporto be formed by vaporization of the water content is reduced. Thus, theamount of water vapor collecting between the layers is reduced,increasing interlayer adhesion.

That is, the printed wiring board according to the second aspect of theinvention has a highly reliable structure, since it hardly undergoesinterlayer delamination.

Further, since the external insulating layer is of a resin, itfacilitates formation of fine patterns. Therefore, the printed wiringboard according to the second aspect of the invention facilitatesformation of a high-density substrate.

As described above, according to the second aspect of the invention,printed wiring boards which hardly undergo interlayer delamination andcan maintain high reliability even if the printed wiring board isallowed to have a higher multilayer structure, can be provided.

Further, the printed wiring board according to the second aspect of theinvention can be utilized, for example, as memory modules, multichipmodules, mother boards, daughter boards and plastic packages.

It is preferred to form two or more internal insulating layers.According to this structure, printed wiring boards having highermultilayer structures and high reliability can be obtained.

The coefficient of water absorption in the internal insulating layer ispreferably 0.1 to 0.3%. Thus, the effects to be brought about accordingto the second aspect of the invention can be secured. It is difficult toform such prepregs as having coefficients of water absorption of lessthan 0.1%; whereas prepregs having coefficients of water absorption ofmore than 0.3% contain too much water to exhibit the effect to bebrought about according to the second aspect of the invention.

A third aspect of the invention is a method of manufacturing a printedwiring board having a plurality of conductive layers which are built upvia insulating layers respectively and are electrically connected to oneanother via interconnecting through holes. The method comprises thesteps of forming conductive layers on a plurality of insulating layersrespectively; laminating and press-bonding the resulting insulatinglayers to form a multilayer substrate; irradiating a laser beam upon themultilayer substrate at interconnecting through hole-forming portions todefine interconnecting through holes such that the bottoms of thesethrough holes reach the conductive layers; fusing solder balls againstthe interconnecting through holes and filling them with the solder.

Actions and effects of the third aspect of the invention will bedescribed.

In the third aspect of the invention, after the insulating layers arelaminated, a laser beam is irradiated to form interconnecting throughholes. Accordingly, interconnecting through holes penetrating all of theinsulating layers are formed by a single hole-defining procedure.Further, there is no need of forming interconnecting throughhole-defining through holes in the respective insulating layersindependently, facilitating formation of interconnecting through holes.

Furthermore, according to the third aspect of the invention,interconnecting through holes having different depths can be formed bythe single hole-defining procedure.

Unlike the prior art, insulating layers need not be positioned forsecuring continuity of the through holes. Further, even smallinterconnecting through holes can be formed accurately.

Further, the interconnecting through holes are filled with a solder, andsolder balls are fused to the openings of the interconnecting throughholes, so that electric currents flowing across the internal conductivelayers can be taken out easily through the solder and solder balls.

The walls of the interconnecting through holes are preferably coveredwith metal plating films, and thus conductivity can be imparted to thesethrough holes.

The conductive layers preferably have a thickness of 10 to 70 μm. Ifthey have a thickness of less than 10 μm, holes are likely to be formedin the conductive layers by the laser beam irradiation; whereas if theyhave a thickness of more than 70 μm, patterning of the conductive layersis likely to be difficult.

The insulating layers are preferably flexible films made of a glassfiber-reinforced resin. Such insulating layers facilitate thehole-defining procedures using laser beam, and besides thinning ofprinted wiring boards can be realized.

As the laser beam 341, for example, a CO₂ laser and an eximer laser canbe used.

As the insulating layer, for example, synthetic resin single substances,resin base materials containing synthetic resins and inorganic fillers,cloth base materials containing synthetic resins and inorganic cloth,etc. can be used. The synthetic resins include, for example, epoxyresins, phenol resins, polyimide resins, polybutadiene resins andfluororesins. Insulating layers formed using such synthetic resins onlyare occasionally laminated as prepregs or solder resists between otherinsulating layers.

Further, the inorganic fillers to be added to the synthetic resinsinclude, for example, glass short fibers, silica powders, mica powders,alumina and carbon. Base materials containing mixtures of syntheticresins and inorganic fillers show high strength compared with those madeof synthetic resin single substances.

Meanwhile, the cloth base materials referred to above mean thosesubstrates made of woven or knitted fabric cloth and synthetic resinssuch as glass-epoxy substrates and glass-polyimide substrates. Suchcloth base materials include those obtained by impregnating the clothwith synthetic resins. Further, materials of the cloth includeglass-fiber cloth, carbon cloth, aramid cloth, etc. As the syntheticresins those as described above are employed.

The conductive layers referred to above mean conductive patterns whichare formed parallel to the surfaces of insulating layers, for example,wiring patterns, pads, lands and terminals. The conductive patterns areformed, for example, by etching metal foils or by metal plating.

The printed wiring board manufactured according to the third aspect ofthe invention can be utilized, for example, as memory modules, multichipmodules, mother boards, daughter boards and plastic packages.

A fourth aspect of the invention is a printed wiring board comprising aninterconnecting through hole penetrating an insulating substrate, acovering pad covering one opening of the interconnecting through hole,and a conductor circuit provided along the peripheral edge of the otheropening which remains open; wherein the covering pad and the conductorcircuit are electrically connected to each other via a metal platingfilm covering the wall of the interconnecting through hole; and a solderball for external connection is bonded onto the surface of the coveringpad.

Actions and effects of the fourth aspect of the invention will bedescribed.

In the fourth aspect of the invention, one opening of eachinterconnecting through hole is covered with a covering pad on which asolder ball is bonded. Accordingly, the covering pad for bonding asolder ball can be located substantially in alignment with theinterconnecting through hole.

Therefore, the area occupied by the interconnecting through holecoincides with the area occupied for bonding the solder ball, so thatthere is no need of securing the area for forming interconnectingthrough holes and the area for bonding solder balls separately, thusachieving high-density packaging of interconnecting through holes andsolder balls.

Further, since the areas to be occupied by the interconnecting throughholes and solder balls are narrowed to afford extra spaces on thesurface of the insulating substrate, conductor circuits and the like canbe formed on such extra spaces, enabling high densification of surfacepackaging on the insulating substrate. Besides, the fourth aspect of theinvention fully satisfies the requirements particularly for multilayerbuild-up type printed wiring boards which require high-density surfacepackaging.

The solder balls are preferably located in alignment with the centralaxes of the interconnecting through holes respectively. Since theinterconnecting through holes and the solder balls can be alignedrespectively, the areas to be occupied by both of them can further benarrowed.

The solder balls may be located at positions offset from theinterconnecting through holes respectively. In this case, larger areasare required for bonding solder balls and for forming theinterconnecting through holes compared with the case where they arealigned. However, they can be located in small areas compared with theprior art where they are located completely separately.

It is preferred that the surface of the insulating substrate is coveredwith a solder resist, and also the interconnecting through holes arefilled with the solder resist. Thus, the conductor circuit formed on thesurface of the insulating substrate and the metal plating films formedon the walls of the interconnecting through holes can be protected frommoisture and flawing. The solder ball-connecting portions are notcovered with the solder resist but are exposed. In the case whereterminal connecting portions for terminals other than solder balls areto be secured, such portions are not covered with the resist but areexposed. The interconnecting through holes may be filled with a fillerof conductive materials such as a solder in place of the solder resist.

A fifth aspect of the invention is a printed wiring board comprising aninterconnecting through hole penetrating an insulating substrate, anannular pad disposed along the peripheral edge of one opening of theinterconnecting through hole so as not to cover the opening, a coveringpad covering the other opening of the interconnecting through hole and aconductor circuit connected to the covering pad; wherein the annular padand the covering pad are electrically connected to each other by a metalplating film covering the wall of the interconnecting through hole; anda solder ball for external connection is bonded onto the surface of theannular pad.

In the fifth embodiment of the invention, an annular pad is locatedalong the peripheral edge of one opening of each interconnecting throughhole, and a solder ball is bonded onto the surface of the pad.Accordingly, the solder ball can be located substantially in alignmentwith the interconnecting through hole. Therefore, the area to beoccupied by the interconnecting through hole coincides with the area tobe occupied for bonding the solder ball, so that there is no need ofsecuring the area for forming interconnecting through holes and the areafor bonding solder balls separately, thus achieving high-densitypackaging of interconnecting through holes and solder balls.

Further, since the areas to be occupied by the interconnecting throughholes and solder balls are narrowed to afford extra spaces on thesurface of the insulating substrate, conductor circuits and the like canbe formed on such extra spaces, enabling high densification of surfacepackaging on the insulating substrate.

It is preferred that the solder balls are located in alignment with thecentral axes of the interconnecting through holes respectively and thateach interconnecting through hole is filled with the solder as a lowerpart of the solder ball. Since the interconnecting through holes and thesolder balls can be aligned respectively as described above, the areasto be occupied by both of them can further be narrowed.

The solder balls may be located at positions offset from theinterconnecting through holes respectively. In this case, larger areasare required for bonding solder balls and for forming theinterconnecting through holes compared with the case where they arealigned. However, they can be located in small areas compared with theprior art where they are located completely separately.

The surface of the insulating substrate is preferably covered with asolder resist. Thus, the conductor circuit formed on the surface of theinsulating substrate can be protected from moisture, flawing, etc. Thesolder ball-connecting portions on the covering pads are not coveredwith the solder resist but are exposed. In the case where terminalconnecting portions for terminals other than solder balls are to besecured, such portions are not covered with the resist but are exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the printed wiring board accordingto a first embodiment of the invention;

FIG. 2 is a cross-sectional view of an insulating layer in the method ofmanufacturing the printed wiring board of the first embodiment;

FIG. 3 is a cross-sectional view continuing from FIG. 2 showing a secondinsulating layer containing interconnecting through holes;

FIG. 4 is a cross-sectional view continuing from FIG. 3 showing thesecond insulating layer in which a metal plating film is formed on thewalls of the interconnecting through holes;

FIG. 5 is a cross-sectional view continuing from FIG. 4 showing thesecond insulating layer on which a black oxide film is formed;

FIG. 6 is a cross-sectional view continuing from FIG. 5 showing thesecond insulating layer on which a prepreg and a copper foil arelaminated;

FIG. 7 is a cross-sectional view continuing from FIG. 6 showing first tothird insulating layers;

FIG. 8 is a cross-sectional view continuing from FIG. 7 showing thefirst to third insulating layers having a first conductive layer formedon the first insulating layer;

FIG. 9 is a cross-sectional view continuing from FIG. 8 showing thefirst to third insulating layers in which interconnecting through holesand connecting holes are formed;

FIG. 10 is a cross-sectional view of the printed wiring board accordingto a second embodiment of the invention;

FIG. 11 is a cross-sectional explanatory drawing of the printed wiringboard according to a third embodiment of the invention;

FIG. 12 is an explanatory drawing showing the process of manufacturingthe printed wiring board according to a fourth embodiment of theinvention;

FIG. 13 is a cross-sectional view of the printed wiring board of thefourth embodiment of the invention;

FIG. 14 is a cross-sectional view of an insulating layer forillustrating the method of forming the first insulating layer of thefourth embodiment;

FIG. 15 is a cross-sectional view continuing from FIG. 14 showing theinsulating layer on which a copper foil is bonded;

FIG. 16 is a cross-sectional view continuing from FIG. 15 showing theinsulating layer on which a conductive layer is formed;

FIG. 17 is a cross-sectional view of the insulating layer forillustrating the method of forming the second insulating layer of thefourth embodiment;

FIG. 18 is a cross-sectional view continuing from FIG. 17 showing theinsulating layer in which a through hole for defining a mounting recessis formed;

FIG. 19 is a cross-sectional view of the insulating layer forillustrating the method of forming the third insulating layer of thefourth embodiment;

FIG. 20 is a cross-sectional view continuing from FIG. 19 showing theinsulating layer on which a copper foil is bonded;

FIG. 21 is a cross-sectional view continuing from FIG. 20 showing theinsulating layer on which a conductive layer is formed;

FIG. 22 is a cross-sectional view continuing from FIG. 21 showing theinsulating layer covered with a solder resist;

FIG. 23 is a cross-sectional view of a multilayer substrate formed bylaminating and press-bonding the first insulating layer, the secondinsulating layer, the third insulating layer and a heat-radiating metalplate;

FIG. 24 is a cross-sectional view continuing from FIG. 23 showing themultilayer substrate containing interconnecting through holes;

FIG. 25 is a cross-sectional view showing the pertinent portion of theprinted wiring board according to a fifth embodiment of the invention;

FIG. 26 is a cross-sectional view of the printed wiring board of thefifth embodiment;

FIG. 27 is a plan view of the printed wiring board of the fifthembodiment;

FIG. 28 is a bottom view of the printed wiring board of the fifthembodiment;

FIG. 29 is an explanatory drawing showing a method of forminginterconnecting through holes in an insulating substrate in the fifthembodiment;

FIG. 30 is an explanatory drawing showing a method of applying chemicalcopper plating treatment to the insulating substrate in the fifthembodiment;

FIG. 31 is an explanatory drawing showing a method of applyingelectrical copper plating treatment to the insulating substrate in thefifth embodiment;

FIG. 32 is an explanatory drawing showing the state of the plating layerformed when a plating solution distributing pinhole is formed in thecovering pad;

FIG. 33 is a cross-sectional view showing the pertinent portion of theprinted wiring board according to a sixth embodiment of the invention;

FIG. 34 is an explanatory drawing of the covering pad in the sixthembodiment;

FIG. 35 is a cross-sectional view showing the pertinent portion of theprinted wiring board according to a seventh embodiment of the invention;

FIG. 36 is an explanatory drawing of the covering pad in the seventhembodiment;

FIG. 37 is a cross-sectional view of the multilayer printed wiring boardaccording to an eighth embodiment of the invention;

FIG. 38 is a cross-sectional view showing the pertinent portion of theprinted wiring board according to a ninth embodiment of the invention;

FIG. 39 is a cross-sectional view showing the pertinent portion of theprinted wiring board according to a tenth embodiment of the invention;

FIG. 40 is an explanatory drawing showing an annular pad in the tenthembodiment;

FIG. 41 is a cross-sectional view of the multilayer printed wiring boardaccording to an eleventh embodiment of the invention;

FIG. 42 is a cross-sectional view of the printed wiring board of theprior art having an even number of conductive layers;

FIG. 43 is an explanatory drawing illustrating the process ofmanufacturing the printed wiring board of the prior art so as to show amethod of forming a conductive layer as the outermost layer;

FIG. 44 is an explanatory drawing continuing from FIG. 43 illustrating amethod of forming interconnecting through holes;

FIG. 45 is a cross-sectional view of the printed wiring board of theprior art having an odd number of conductive layers;

FIG. 46 is an explanatory drawing illustrating the method ofmanufacturing the printed wiring board of the prior art having an oddnumber of conductive layers, in which second to fifth conductive layersare formed;

FIG. 47 is an explanatory drawing continuing from FIG. 46 showing theinsulating layer exposed by removing the fifth conductive layer;

FIG. 48 is an explanatory drawing continuing from FIG. 47 showing theinsulating layer in which interconnecting through holes are defined inthe second insulating layer;

FIG. 49 is an explanatory drawing continuing from FIG. 48 showing theinsulating layers having first to fifth conductive layers respectively;

FIG. 50 is an explanatory drawing continuing from FIG. 49 showing theinsulating layers having interconnecting through holes formed throughthe outermost insulating layer; and

FIG. 51 is an explanatory drawing showing the process of manufacturingthe printed wiring board according to another example of the prior art.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

The printed wiring board of the embodiment according to the first aspectof the invention will be explained referring to FIGS. 1 to 9.

The printed wiring board 41 of the first embodiment has three conductivelayers 11 to 13 which are built up via insulating layers 21 to 23respectively, as shown in FIG. 1. The conductive layers 11 to 13 areelectrically connected to one another by interconnecting through holes31 and 32.

The first conductive layer 11 is a component connecting layer on whichan electronic component 61 is mounted and leads electric currents in andout of the component 61.

The second conductive layer 12 is an electric current transmitting layerfor transmitting internal electric currents of the printed wiring board41.

The third conductive layer 13 is an external connecting layer forconnecting external connecting terminals 7 for leading electric currentsin and out of the printed wiring board 41. The surface of the third andoutermost conductive layer 13 is covered with the third insulating layer23 with the external connecting terminals 7 being exposed. The externalconnecting terminals 7 are solder balls.

Next, the method of manufacturing the above printed wiring board will bedescribed.

First, as shown in FIG. 2, copper foils 1 are bonded to the upper sideand lower side of the second insulating layer 22, and theninterconnecting through holes 32 are formed through the insulating layer22 and the copper foils 1 by drilling, followed by etching of the copperfoils 1 to form conductive layers 12 and 13, as shown in FIG. 3.

Subsequently, as shown in FIG. 4, the wall of each interconnectingthrough hole 32 is subjected to chemical copper plating and electriccopper plating to form a metal plating film 5. In this step, thesurfaces of the conductive layers 12 and 13 are covered with the metalplating films 5.

Next, as shown in FIG. 5, a resin paste 2 is packed into theinterconnecting through holes 32 by means of printing, and then blackoxide films 10 are formed on the surfaces of the conductive layers 12and 13. The black oxide films 10 are formed so as to enhance adhesionbetween the conductive layers and insulating layers to be laminatedthereon respectively.

Then, as shown in FIG. 6, a prepreg 20 and a copper foil 1 are laminatedon the surface of the conductive layer 12, while only a prepreg 20 islaminated on the surface of the conductive layer 13, followed by hotpress-bonding of the resulting laminate. Thus, as shown in FIG. 7, thesecond insulating layer 22 has insulating layers 21 and 23 formed on theupper side and lower side and a copper foil 1 is bonded onto the surfaceof the insulating layer 21. Subsequently, the copper foil 1 is etched toform a first conductive layer 11, as shown in FIG. 8.

As shown in FIGS. 8 and 9, a laser beam 6 is irradiated upon theinsulating layer 21 at the interconnecting through hole-forming portions39 to form interconnecting through holes 31 reaching the internalconductive layer 12. The laser beam 6 is also irradiated upon theinsulating layer 23 at the bonding hole-forming portions 30 to formbonding holes 3 reaching the internal conductive layer 13.

Subsequently, as shown in FIG. 10, chemical copper plating treatment andelectric copper plating treatment are carried out to form a metalplating film 5 on the wall of each interconnecting through hole 31. Asolder ball is supplied into each bonding hole 3 to form an externalconnecting terminal 7 connected to the conductive layer 13.

Thus, the printed wiring board 41 can be obtained.

In the above printed wiring board 41, an electronic component 61 isbonded to the surface of the first insulating layer 21 using a bondingagent 611 such as a solder. The electronic component 61 is electricallyconnected to the conductive layer 11 using bonding wires 62.

Further, the external connecting terminals 7 are connected to pads onthe surface of a mother board 8 (FIG. 1).

Next, actions and effects of this embodiment will be described.

The printed wiring board 41 of this embodiment has three conductivelayers 11 to 13 formed between three insulating layers 21 to 23,respectively, as shown in FIG. 1. The second insulating layer 22 ofthese three insulating layers 21 to 23 is the central insulating layerhaving the same number of insulating layers on the upper side and thelower side. Accordingly, as shown in FIGS. 6 and 7, no warping occurs inthe printed wiring board when prepregs 20 for forming insulating layersare press-bonded.

In addition, the conductive layers 11 and 14 can be built up efficientlyon the upper and lower sides of the central insulating layer 22.

Therefore, the printed wiring board 41 of this embodiment has thestructure which facilitates building of the three conductive layers 11to 13.

Furthermore, the third and last conductive layer 13 is covered with thethird and outermost insulating layer 23. Accordingly, the thirdconductive layer 13 is embedded in the printed wiring board 41. Howeverthe external connecting terminals 7 connected to the third conductivelayer 13 are exposed through the bonding holes 3 of the third andoutermost insulating layer 23, so that leading of electric currents inand out of the printed wiring board 41 can be carried out through theseexternal connecting terminals 7.

The external connecting terminals 7 are solder balls, so that theyfacilitate bonding with the internal conductive layer 13 and can connectthe printed wiring board 41 stably to an external mother board 8.

Meanwhile, in the method of manufacturing the printed wiring board ofthis embodiment, a prepreg 20 and a copper foil 1 for forming the firstconductive layer are laminated on the surface of the second conductivelayer 12, while only a prepreg 20 is laminated onto the surface of thethird conductive layer 13 with no copper foil, as shown in FIG. 6.

When the prepregs 20 and the copper foil 1 are press-bondedrespectively, the first insulating layer 21 and the third insulatinglayer 23 can be formed simultaneously by this press-bonding treatment.Accordingly, the second insulating layer 22 already laminated into onebody receives, on the upper side and lower side, thermal stress evenlyfrom the surface prepregs 20 during the press-bonding, so that nowarping occurs in the printed wiring board 41.

Further, the third and last conductive layer 13 is covered on thesurface with the insulating layer 23. In this state, no electric currentcan be led in and out through the third conductive layer 13. However,bonding holes 3 are defined in the outermost insulating layer 24, andthe external connecting terminals 7 are exposed through the bondingholes 3. Thus, electric currents can be led in and out through the thirdand final conductive layer 13 through these external connectingterminals 7.

Second Embodiment

The printed wiring board of the second embodiment has five conductivelayers 11 to 15 which are built up as shown in FIG. 10.

The first conductive layer 11 is a component connecting layer on whichan electronic component 61 is mounted and leads electric currents in andout of the component 61.

The second to fourth conductive layers 12 to 14 are electric currenttransmitting layers for transmitting internal electric currents of theprinted wiring board 42.

The fifth conductive layer 15 is an external connecting layer forconnecting external connecting terminals 7 for leading electric currentsin and out of the printed wiring board 42. The surface of the fifthconductive layer 15 is covered with the fifth and outermost insulatinglayer 25 with the external connecting terminals 7 being exposed.

When a printed wiring board 42 of this embodiment is manufactured,conductive layers 13 and 14 and interconnecting through holes 33 areformed in the third and central insulating layer 23 in the same manneras in the first embodiment. Then, insulating layers 22 and 24 arelaminated on the surfaces of the conductive layers 13 and 14, and alsoconductive layers 12 and 15 are formed on the insulating layers 22 and24, respectively. Subsequently, interconnecting through holes 32 and 34are defined in the insulating layers 22 and 24, respectively, and ametal plating film 5 is formed on the walls of these through holes 32and 34.

Next, a first insulating layer 21 and a conductive layer 11 are formedon the surface of the conductive layer 12, followed by formation ofinterconnecting through holes 31, whereas a fifth insulating layer 25 isformed on the surface of the conductor layer 15, followed by formationof bonding holes 3, in the same manner as in the first embodiment.

Thus, the printed wiring board 42 having five conductive layers 11 to 15can be obtained.

The other constitutions are the same as those in the first embodiment.

In the second embodiment, effects similar to those in the firstembodiment are obtained.

Third Embodiment

The printed wiring board of the embodiment according to the secondaspect of the invention will be explained referring to FIG. 11.

As shown in FIG. 11, the printed wiring board 101 of the thirdembodiment has an internal insulating substrate 116 having on each sidea conductor circuit 115, an internal insulating layer 117 laminated onthe surface of the internal insulating substrate 116 and an externalinsulating layer 118 laminated on the internal insulating layer 117.Each internal insulating layer 117 has on the surface an internalconductor circuit 125, while each external insulating layer 118 has onthe surface an external conductor circuit 135.

The internal insulating layer 117 is of a glass cloth-reinforcedprepreg, whereas the external insulating layer 118 is of a resin.

The internal insulating layer 117 is a prepreg prepared by impregnatinga glass cloth with an epoxy resin, and the external insulating layer 118is an epoxy resin.

Next, the printed wiring board 101 of this embodiment will be describedbelow specifically.

The internal insulating substrate 116 in the printed wiring board 101has conductor circuits 115 on both sides. The internal insulatingsubstrate 116 has interconnecting through holes 110 embedded with asolder 111, and these through holes 110 secure electrical continuitybetween the internal conductor circuits 115.

The internal conductor circuits 115 are each composed of a copper foilpattern 112 and a plating film 113 formed on the copper foil pattern112.

The internal insulating substrate 116 has on each side an internalinsulating layer 117. The internal insulating layer 117 contains blindvia holes 120 each having a plating film 123 formed on the wall.

Further, an internal conductor circuit 125 is formed on the surface ofeach internal insulating layer 117. The internal conductor circuit 125is composed of a copper foil pattern 122 and a plating film 123.

The external insulating layer 118 is formed on the surface of eachinternal insulating layer 117. The external insulating layer 118contains via holes 130 having plating films 133 on the wallsrespectively. Further, the external insulating layer 118 has on thesurface an external conductor circuit 135 composed of a copper foilpattern 132 and a plating film 133.

The surface of the external insulating layer 118 is covered partly withsolder resist and has lands for mounting solder balls, which are notshown.

Next, a method of manufacturing the above printed wiring board 101 willbe described. According to this method, the internal insulating layers117, external insulating layers 118, conductor circuits andinterconnecting through holes are formed according to the build-upprocess and the additive process.

Specifically, a copper clad laminate having copper foils on the surfacesis prepared. Next, the copper foils are patterned by etching to formcopper foil patterns 112, followed by formation of interconnectingthrough holes 110 through the resulting copper-clad laminate.

Subsequently, a plating film 113 is formed by electroless copper platingon the walls of the interconnecting through holes 110 and on the copperfoil patterns 112. Thus, conductor circuits 115 connected to theinterconnecting through holes can be obtained. A solder 111 is thenembedded in the interconnecting through holes 110.

Next, a prepreg and a copper foil are laminated and press-bonded on eachside of the internal insulating substrate 116. Thus, the copper foilscan be laminated on both sides of the internal insulating substrate 116via internal insulating layers 17 respectively.

The copper foils are then subjected to patterning to form copper foilpatterns 122, followed by laser beam irradiation upon the internalinsulating layers 117 to form blind via holes 120. As the laser beam, aneximer laser having a wavelength of 248 nm and an output power of 50 Wis used.

The walls of the blind via holes 120 and the copper foil patterns 122are subjected to electroless plating for forming plating films 123 onthem.

Next, in the same manner as in the case where the internal insulatinglayers 117 and the internal conductor circuits 125 are formed, anexternal insulating layer 118 containing via holes 130 and an externalconductor circuit 135 comprising a copper foil pattern 132 and a platingfilm 133 are formed on the surface of each internal insulating layer117.

As described above, the printed wiring board 101 is obtained.

Next, actions and effects of this embodiment will be described.

In the printed wiring board 101 of this embodiment, the internalinsulating layers 117 are of glass cloth-reinforced prepregs, whereasthe external insulating layers 118 are of a resin. Thus, the coefficientof water absorption in the internal insulating layers 17 can be lowered.

Since the absolute amount of water contained in the internal insulatinglayers 117 is reduced, the amount of water vapor collecting between thelayers is reduced, enhancing adhesion between the internal insulatinglayers 117 and the internal insulating substrate 116, and between theinternal insulating layers 117 and the external insulating layers 118.

That is, the printed wiring board 101 of this embodiment has a highlyreliable structure which hardly undergoes interlayer delamination.

As described above, a printed wiring board 101 which hardly undergoesinterlayer delamination and can maintain high reliability even if it hasa multilayer structure can be obtained according to this embodiment.

The printed wiring board 101 illustrated in this embodiment is of thestructure in which internal insulating layers 117 are laminated on bothsides of the internal insulating substrate 116. However, like actionsand effects can be obtained even when a printed wiring board having aninternal insulating layer on one side only is prepared and a glasscloth-reinforced prepreg is used as the internal insulating layer.

Like actions and effects can also be obtained for printed wiring boardshaving higher multilayer structures other than those having 6 layers,e.g., 8-layer substrate, 10-layer substrate.

Fourth Embodiment

The method of manufacturing the printed wiring board of the embodimentaccording to the third aspect of the invention will be describedreferring to FIGS. 12 to 24.

The printed wiring board 209 to be manufactured according to thisembodiment has, as shown in FIG. 13, a multilayer substrate 201containing first to third insulating layers 211 to 213 and twoconductive layers 231 and 233 formed thicknesswise with respect to theinsulating layers; through holes 210, 220 and 230 formed to penetrateall of the first to third insulating layers 211 to 213; and aheat-radiating metal plate 202 provided on the upper side of themultilayer substrate 201 so as to cover the through holes 210, 220, 230.

The through holes 210, 220 and 230 and the heat-radiating metal plate202 define a mounting recess 214 for mounting an electronic component298. The multilayer substrate 201 is provided with interconnectingthrough holes 217 and 218 communicating with the conductive layers 231and 233, respectively.

Solder balls 251 and 252 are located on the multilayer substrate 201 onthe side on which the mounting recess 214 opens. One solder ball 251 isconnected to the lower opening of the interconnecting through hole 217.The solder ball 251 connects, via the interconnecting through hole 217,the conductive layer 231 provided in the multilayer substrate 201 with amother board 295. The other solder ball 252 is connected to theconductive layer 233 provided on the lower side of the multilayersubstrate 210 to connect the conductive layer 233 to the mother board295.

The solder balls 251 and 252 are fused to the terminals 296 and 297provided on the surface of the mother board 295.

Next, the outline of the method of manufacturing the printed wiringboard 209 of this embodiment will be described referring to FIG. 12.First, in step S1, conductive layers 231 and 233 are formed on a numbern of insulating layers 211 to 213 (FIGS. 16, 18 and 21). Subsequently,in steps S2 and S3, the insulating layers 211 to 213 are laminated andpress-bonded to form a multilayer substrate 201 (FIG. 23). Subsequently,in step S4, laser beam 208 is irradiated upon the multilayer substrate201 at interconnecting through hole-forming portions to defineinterconnecting through holes 217 and 218 such that the bottoms of thesethrough holes reach the conductive layers 231 and 233, respectively(FIG. 24). In step S5, solders 251 and 252 are packed into theinterconnecting through holes 217 (FIG. 12).

Next, the method of manufacturing the above printed wiring board 209will be described in detail referring to FIGS. 14 to 24.

First, a flexible film made of a glass-fiber reinforced epoxy materialis prepared as an insulating layer. The flexible film is a flexiblebelt-like film having a thickness of 0.05 mm and a width of 2.5 to 15cm. This flexible film is preliminary rolled into a plurality of webrolls.

Next, the flexible film is delivered as the insulating layer from one ofthe rolls. Then, as shown in FIG. 14, an insulating adhesive 262 whichis of a thermoplastic glass fiber-reinforced epoxy material is bonded tothe lower side of the delivered insulating layer 211, and a through hole210 is then formed by punching substantially at the center of theresulting insulating layer 211, as shown in FIG. 15. Subsequently, acopper foil 232 having a thickness of 35 μm is bonded to the lower sideof the insulating layer 211 via the insulating adhesive 262, as shown inFIG. 15.

Then, as shown in FIG. 16, a conductive layer 231 is formed from thecopper foil by means of irradiation and etching, and an Ni/Au platingfilm is formed to cover the surface of the conductive layer 231. Thus, afirst insulating layer 211 serving as an upper layer of the multilayersubstrate 201 is obtained.

As shown in FIG. 17, insulating adhesives 263 and 264 which are of thesame material as that of the insulating adhesive 262 is adhered to theupper and lower sides of the flexible film serving as the insulatinglayer 212 delivered from another roll. Subsequently, as shown in FIG.18, a through hole 220 is formed by punching processing substantially atthe center of the insulating layer 212. Thus, a second insulating layer212 serving as an intermediate layer of the multilayer substrate isobtained.

As shown in FIG. 19, an insulating adhesive 265 which is of the samematerial as that of the insulating adhesive 262 is adhered to the lowerside of the flexible film serving as the insulating layer 213 deliveredfrom another roll.

Subsequently, as shown in FIG. 20, the lower side of the insulatinglayer 213 is covered with a copper foil 232.

Next, as shown in FIG. 21, the copper foil 230 is subjected topatterning by means of irradiation and etching to form a conductivelayer 233, and then an Ni/Au plating film is formed on the surface ofthe conductive layer 233.

As shown in FIG. 22, the lower side of the insulating layer 213 iscovered with a solder resist 266. Thus, a third insulating layer 213serving as a lower layer of the multilayer substrate 201 is obtained.

Subsequently, as shown in FIG. 23, the first insulating layer 211, thesecond insulating layer 212 and the third insulating layer 213 arelaminated and press-bonded with heating by the insulating adhesives 262to 264. Thus, a multilayer substrate 201 having three layers isobtained.

A copper heat-radiating metal plate 202 having a thickness of 1.0 mm ispress-bonded to the upper side of the multilayer substrate 201 via aninsulating adhesive 261, and thus a mounting recess 214 is defined bythe through holes 210, 220 and 230 and the heat-radiating metal plate202 covering the upper side of the through holes.

Next, a laser beam 208 is irradiated upon the multilayer substrate 201at interconnecting through hole-forming portions. As the laser beam, aCO₂ laser is employed. Thus, interconnecting through holes 217 and 218are formed in the multilayer substrate 201 so that the bottoms of thethrough holes 217 and 218 reach the conductive layers 231 and 233,respectively.

Subsequently, as shown in FIG. 13, a solder 254 is packed into the deepinterconnecting through holes 217, and then solder balls 251 and 252 arefuse-bonded to the lower openings of the interconnecting through holes217 and the lower openings of the shallow interconnecting through holes218.

Thus, a printed wiring board 209 is obtained.

Then, as shown in FIG. 13, an electronic component 298 is mounted in themounting recess 214 using a die-bonding material 269 such as a silverpaste and a solder. Next, the electronic component 298 and the tips ofthe conductive layers 231 and 233 are bonded using wires 281, and thenthe space in the mounting recess 214 is filled with a sealing resin 206.

Next, actions and effects of this embodiment will be described.

In this embodiment, as shown in FIGS. 23 and 24, interconnecting throughholes 217 and 218 are formed by irradiating the laser beam 208 afterlamination of the first to third insulating layers 211 to 213.Accordingly, the interconnecting through holes 217 and 218 penetratingthrough the insulating layers 212 and 213 can be formed by a singlehole-defining procedure. Further, there is no need of forming throughholes for forming the interconnecting through holes for the respectiveinsulating layers.

Further, interconnecting through holes 217 and 218 having differentdepths can be formed by a single hole-defining procedure.

There is no need of positioning the insulating layers for securingcontinuity of the through holes as required in the prior art. Further,even small interconnecting through holes can be formed accurately.

Since the thickness of the conductive layers 231 and 233 are 35 μm,interconnecting through holes 217 and 218 can be formed without formingholes in the conductive layers 231 and 233.

Fifth Embodiment

The printed wiring board of the embodiment according to the fourthaspect of the invention will be described referring to FIGS. 25 to 32.

The printed wiring board 305 of the fifth embodiment has aninterconnecting through hole 302 penetrating an insulating substrate307. One opening of the interconnecting through hole 302 is covered by acovering pad 311, while the other opening remains open and has aconductor circuit 316 along the opening edge.

The covering pad 311 and the conductor circuit 316 are electricallyconnected via a metal plating film 323 covering the wall of theinterconnecting through hole 302.

A solder ball 303 for external connection is bonded onto the surface ofthe covering pad 311. The solder ball 303 is aligned with the centralaxis A of the interconnecting through hole 302. The surface of theinsulating substrate 307 is covered with a solder resist 306, and theinterconnecting through hole 302 is packed with the solder resist 306.

Further, as shown in FIGS. 26 and 27, the upper side of the insulatingsubstrate 307 is provided with an annular land 312 formed along theopening edge of the interconnecting through hole 302 and a mounting pad355 for mounting an electronic component 350. A bonding pad 317 forbonding wires 351 to be connected to the electronic component 350 areprovided around the mounting pad 355. The electronic component 350 andthe bonding wires 351 are protected by a sealing resin 359.

Meanwhile, as shown in FIGS. 26 and 28, a multiplicity of covering pads311 for bonding solder balls 303 are provided on the lower side of theinsulating substrate 307 in alignment with the interconnecting throughholes 302 respectively. The solder balls 303 are fused to pads 381 of amother board 308 or the like.

Next, the method of manufacturing the above printed wiring board 305will be described.

First, an insulating substrate 307 composed of an epoxy, polyimide orbismaleimidotriazine resin and a glass fiber or glass cloth reinforcingmaterial is prepared. A copper foil is bonded onto the surface of theinsulating substrate 307.

The insulating substrate 307 is then subjected to treatments such aslight exposure and etching to effect patterning of the copper foil 321,as shown in FIGS. 29 and 26, and form a conductor circuit 316, a bondingpad 317 and a mounting pad 355. Simultaneously, covering pads 311 forcovering interconnecting through hole-forming portions 320 and annularlands 312 surrounding the peripheral edges of the interconnectingthrough hole-forming portions 320 are formed on one side and on theother side of the insulating substrate 307, respectively.

Next, as shown in FIG. 29, laser beam 341 is irradiated upon theinsulating substrate 307 at the interconnecting through hole-formingportions 320. A laser irradiator 342 is moved horizontally along theplane of the insulating substrate 307 to emit the laser beam 341 at thespots corresponding to the interconnecting through hole-forming portions320. As the laser beam 341, it is preferred to use a CO₂ laser havinggreat output power energy, an eximer laser which gives less thermalinfluence or the like.

Formation of the interconnecting through holes 302 by irradiation of thelaser beam 341 is carried out by vaporizing and removing the insulatingsubstrate 307 at the corresponding portion with the high energy of thelaser beam 341 to bore gradually into the insulating substrate 307. Uponthe reaching of the tip of the laser beam 341 to each covering pad 311covering the bottom, the laser beam 341 is reflected by the copper foilserving as the covering pad 311, and irradiation of the laser beam 341is then terminated. The interconnecting through holes 302 have adiameter of, for example, 0.1 mm.

Then, as shown in FIG. 30, a thin chemical copper plating film 321having a thickness of about 1 μm is formed on portions where metalplating films are to be formed, i.e., on the patterned copper foil 321and the walls of the interconnecting through holes 302, followed bycleaning of the thus treated insulating substrate 307.

Next, as shown in FIG. 31, the surface of the insulating substrate 307including the walls of the interconnecting through holes 302 issubjected to electrical copper plating treatment. The electrical copperplating treatment is carried out by immersing the insulating substrate307 together with an anode into an electrical plating bath with thechemical copper plating film being connected to the cathode via anelectric lead 319. The electrical plating bath contains copper sulfateand has a bath temperature of 60° C. In this state, an electric currenthaving a density of 0.8 to 1.4 A/dm² is applied across the chemicalplating film 323 for 20 minutes.

Thus, the copper melts out of the cathode surface to deposit on thesurface of the chemical plating film serving as the anode, forming acopper metal plating film 322 on the walls of the interconnectingthrough holes 302 and also covering the surfaces of the covering pads311, conductor circuits 316, lands 312, bonding pads 317 and mountingpad 355 (see FIG. 27). Incidentally, the electric lead 319 is removed bymeans of etching, laser irradiation or the like, after the platingtreatment.

Pinholes 313 can be formed at the centers of the covering pads 311, asshown in FIG. 32, since the laser beam energy is high at the center andlow around the peripheral portion. These pinholes 313 serve asdistribution channels of the plating solution, as will be describedlater, to allow sufficient distribution of the plating solution in andout of the interconnecting through holes, enabling formation of themetal plating film 322 uniformly on the wall of each interconnectingthrough hole 302.

Next, as shown in FIG. 26, the surface of the insulating substrate 307is covered with a solder resist 306. By this treatment, theinterconnecting through holes 302 are packed with the solder resist 306.Meanwhile, the surfaces of the solder ball bonding portions of thecovering pads 311, bonding pads 317 and mounting pad 355 are exposedwithout being covered with the resist 306.

Then, solder balls 303 are supplied to the surfaces of the covering pads311 with the side of the insulating substrate 307 on which the coveringpads 311 are formed facing upward, followed by fusing of the solderballs 303 with heating to bond the solder balls 303 with the coveringpads 311, respectively.

Subsequently, an electronic component 350 is mounted on the surface ofthe mounting pad 355 using a bonding agent such as a silver paste and isconnected to the bonding pads 317 with bonding wires 351. The electroniccomponent 350 and the bonding wires 351 are then sealed with a sealingresin 359.

As described above, the printed wiring board 305 shown in FIGS. 25 to 28can be obtained.

Now, actions and effects of this embodiment will be described.

In the printed wiring board 305 of this embodiment, one opening of eachinterconnecting through hole 302 is covered with a covering pad 311 onwhich a solder ball 303 is bonded. Accordingly, the covering pad 311 forbonding the solder ball 303 can be substantially aligned with theinterconnecting through hole 302.

Therefore, the area to be occupied by the interconnecting through holecoincides with the area to be occupied for bonding the solder ball, sothat high-density packaging of the interconnecting through holes 302 andthe solder balls 303 is achieved.

Further, the areas to be occupied by the interconnecting through holes302 and solder balls 303 can be narrowed to afford extra spaces on thesurface of the insulating substrate 307. Accordingly, conductor circuitsand the like can be formed on such extra spaces, enabling highdensification of surface packaging on the insulating substrate.

Meanwhile, as shown in FIG. 29, since the interconnecting through holes302 are formed by irradiation of the laser beam 341, fineinterconnecting through holes 302 can be formed easily and accurately,realizing much higher density packaging.

Sixth Embodiment

The sixth embodiment is an embodiment of the fourth aspect of theinvention.

In the printed wiring board 305 of this embodiment, the solder balls 303are offset from the respective interconnecting through holes 302, asshown in FIG. 33.

As shown in FIG. 34, one opening of each interconnecting through hole302 is covered with an ellipsoidal covering pad 314. On the surface ofthis covering pad 314 is bonded a solder ball 303 at a position offsetfrom the central axis of the interconnecting through hole 302. Thesolder ball 303 is located to overlap with at least a portion of theopening of the interconnecting through hole 302.

The other constitutions are the same as those in the fifth embodiment.

In this embodiment, since the solder balls 303 are located at positionsoffset from the central axis of the interconnecting through holes 302respectively, a larger area is required for bonding solder balls and forforming the interconnecting through holes compared with the fifthembodiment. However, since each solder ball 303 is bonded to a part ofthe covering pad 314 covering the opening of each interconnectingthrough hole 302 in this embodiment, the solder ball bonding area andthe interconnecting through hole-forming area need not be formedcompletely separately unlike in the prior art. Therefore, according tothe present invention, not only high-density packaging ofinterconnecting through holes and solder balls but also high-densitywiring on the surface of the insulating substrate can be realized.

Seventh Embodiment

The seventh embodiment is an embodiment of the fourth aspect of theinvention.

In the printed wiring board 305 of the seventh embodiment, each solderball 303 is bonded at a position spaced slightly away from theinterconnecting through hole 303, as shown in FIG. 35.

As shown in FIG. 36, the solder ball 303 is bonded on the surface of anellipsoidal covering pad 315 at a position adjacent to theinterconnecting through hole 302.

The other constitutions are the same as those in the sixth embodiment.

In this embodiment, since each solder ball 303 is bonded at a positionadjacent to the interconnecting through hole 302, a large area isrequired for bonding solder balls and for forming the interconnectingthrough holes compared with the prior art. However, since each solderball 303 is bonded to a part of the covering pad 315 covering theopening of the interconnecting through hole 302 in this embodiment, notonly high-density packaging but also high-density wiring on the surfaceof the insulating substrate can be realized like in the sixthembodiment.

Eighth Embodiment

The eighth embodiment is an embodiment of the fourth aspect of theinvention.

The printed wiring board 305 of this embodiment is a multilayersubstrate 370 formed by laminating a plurality of insulating substrates307, as shown in FIG. 37.

The printed wiring board 305 has interconnecting through holes 302 forelectrically connecting the layers of the multilayer substrate 370. Theopenings of the interconnecting through holes 302 on the lower side ofthe substrate 370 are covered with covering pads 311, 314 and 315located at different positions with respect to the through holes 302respectively. The openings of the interconnecting through holes 302 onthe upper side remain open, and a conductor circuit 316 is formed alongthe opening edge of each through hole 302. Incidentally, some of theinterconnecting through holes 302 penetrate the multilayer substrate370, and some do not.

The covering pads 311, 314 and 315 are electrically connected to theconductor circuits 316 by the metal plating films 322 covering the wallsof the interconnecting through holes 302. A solder ball 303 to beconnected to a pad 381 of a mother board 308 and or like is bonded tothe surface of each covering pad 311.

A solder ball 303 is bonded onto the surface of each covering pad 311 tobe aligned with the central axis A of the interconnecting through hole302 (see FIG. 25). A solder ball 303 is bonded to the surface of anothercovering pad 314 at a position offset from the central axis of theinterconnecting through hole 302 and overlapping with theinterconnecting through hole 302 (see FIG. 34). A solder ball 303 isbonded onto the surface of another covering pad 315 at a position offsetfrom the central axis of the interconnecting through hole 302 and notoverlapping with the interconnecting through hole 302, i.e. at aposition adjacent to the interconnecting through hole (see FIG. 36).

The printed wiring board 305 is provided with a mounting recess 358opening stepwise substantially at the center. An electronic component350 is mounted at the bottom of the mounting recess 358. The electroniccomponent 350 is electrically connected to bonding pads 317 exposed tothe step-like mounting recess 358 by bonding wires 351. The inner spaceof the mounting recess 358 is sealed by a sealing resin 359.

A conductor circuit 316 is formed on the surface of each insulatingsubstrate 307. Each insulating substrate 307 is covered on the surfacewith a solder resist 306. The interconnecting through holes 324 and 325are packed with the solder resist 306. The insulating substrates 307 arebonded to one another with bonding materials 379 such as prepregs.

The other constitutions are the same as those in the fifth embodiment.

In this embodiment, the multilayer substrate 370 formed by laminating aplurality of insulating substrates 307 contains interconnecting throughholes 302, some of which penetrate all of the insulating substrates 307and some of which do not, for electrically connecting the layers, thusenabling formation of conductor circuits 316 with high density in theform of multilayer. Further, it is possible to form lager numbers ofinterconnecting through holes and covering pads and to bond a largernumber of solder balls 303.

Ninth Embodiment

The ninth embodiment is an embodiment of the fifth aspect of theinvention.

The printed wiring board 305 of this embodiment is provided with anannular pad 313 along the peripheral edge of one opening of eachinterconnecting through hole 302, and a solder ball 303 is bonded ontothe surface of the pad 313, as shown in FIG. 38.

That is, one opening of each interconnecting through hole 302 remainsopen and has an annular pad 413 applied along the peripheral edge.Meanwhile, the other opening of the interconnecting through hole 302 iscovered with a covering pad 314. The covering pad 314 is connected to aconductor circuit 316.

The solder ball 303 is aligned with the central axis A of theinterconnecting through hole 302. The interconnecting through hole 302is filled with a solder 330 at a lower part of the solder ball 303. Thesolder 330 is formed by a part of the solder ball 303 melted to flowinto the interconnecting through hole 302, when it is fused onto theannular pad 313.

The interconnecting through hole 302 is preferably filled completelywith the solder 330. Thus, electrical continuity can be secured betweenthe upper side and lower side of the interconnecting through hole 302.In order to fill the solder 330 throughout the interconnecting throughhole 302, it is convenient to apply a flux onto the metal plating film321 formed on the wall of the interconnecting through hole 302 or applya solder paste on the wall of the interconnecting through hole 302before the solder ball 303 is fused with heating. The surface of theinsulating substrate 307 is covered with a solder resist 306. The otherconstitutions are the same as those in the fifth embodiment.

In this embodiment, since an annular pad 413 is provided along theperipheral edge of one opening of each interconnecting through hole 302,and a solder ball 303 is bonded onto the surface of the annular pad 313,the solder ball 303 can be substantially aligned with theinterconnecting through hole 302. Accordingly, the area necessary forthe interconnecting through holes 302 and the area necessary for bondingsolder balls 303 coincide with each other, achieving formation ofinterconnecting through holes and solder balls with high density.

Further, since the area to be occupied by the interconnecting throughholes 302 and the solder balls 303 is reduced to afford extra spaces onthe surface of the insulating substrate 307, conductor circuits, etc.can be formed on such extra spaces, enabling high densification ofsurface packaging on the printed wiring board.

Furthermore, the solder 330, which is embedded in the interconnectingthrough hole 302 as a part of the solder ball 303, provides highreliability in the electrical continuity between the interconnectingthrough hole 302 and the solder ball 303.

The same other effects as in the fifth embodiment can be obtained.

Tenth Embodiment

Tenth embodiment is an embodiment of the fifth aspect of the invention.

In the printed wiring board 305 of this embodiment, a solder ball 303 isbonded at a position adjacent to each interconnecting through hole 302,as shown in FIG. 39.

An oblong annular pad 310 is provided along the peripheral edge of oneopening of each interconnecting through hole 302, as shown in FIG. 40. Asolder ball 303 is bonded onto the surface of this annular pad 310 at aposition offset from the central axis of the interconnecting throughhole 302.

The other constitutions are the same as those in the fifth embodiment.

Since the solder ball 303 is located at a position offset from thecentral axis of each interconnecting through hole 302 in thisembodiment, a larger area is necessary for bonding solder balls and forforming interconnecting through holes 302 than in the ninth embodiment.

However, since each solder ball 303 is bonded to a part of the annularpad 310 provided along the peripheral edge of the opening of eachinterconnecting through hole 302, in this embodiment, there is no needof forming the solder ball bonding areas and interconnecting throughhole forming areas independently unlike the prior art. Therefore,according to the present invention, not only high-density packaging ofinterconnecting through holes and solder balls but also high-densitywiring on the surface of the printed wiring board can be realizedcompared with the prior art.

The tenth embodiments exhibits the same other effects as in the ninthembodiment.

Eleventh Embodiment

The eleventh embodiment is an embodiment of the fifth aspect of theinvention.

The printed wiring board 305 of this embodiment is a multilayersubstrate 370 comprising laminating a plurality of insulating substrates307, as shown in FIG. 41.

The printed wiring board 305 has interconnecting through holes 302, someof which penetrate all of the insulating substrates 307 and some ofwhich do not, for electrically connecting the layers of the multilayersubstrate 370. The openings of the interconnecting through holes 302 onone side of the wiring board 305 remain open and are provided withannular pads 413 and 310 having different shapes, respectively. Theopenings of the interconnecting through holes 302 on the other side ofthe wiring board 305 are covered with covering pads 314. The coveringpads 314 are connected to conductor circuits 316 respectively.

The annular pads 413 and 310 are electrically connected to the coveringpads 314 through the metal plating films 322 covering the walls of theinterconnecting through holes 302. Solder balls 303 to be connected topads 381 of a mother board 308 and the like are bonded onto the surfacesof the a annular pads 413 and 310, respectively.

A solder ball 303 is bonded onto the surface of each annular pad 413 inalignment with the central axis A of each interconnecting through hole302 (see FIG. 38). Meanwhile, solder balls 303 are bonded onto thesurfaces of other annular pads 310 at positions offset from the centralaxes of the interconnecting through holes 302 and not overlapping withthe through holes 302, respectively, i.e., at positions adjacent to theinterconnecting through holes 302 (see FIGS. 39 and 40).

A heat-radiating plate 304 is bonded with a bonding material 390 such asa prepreg onto the other side of the multilayer substrate 370 acrossfrom the side on which the solder balls 303 are bonded. Theheat-radiating plate 304 covers a mounting hole 357 defined stepwise inthe multilayer substrate 370 and has on its surface an electroniccomponent 350 adhered using a bonding agent 379 such as a solder paste.

The other constitutions are the same as those in the eighth embodiment.

In this embodiment, the multilayer substrate formed by laminating aplurality of insulating substrates 307 contains interconnecting throughholes 302 for electrically connecting the layers. Accordingly,high-density packaging of conductor circuits 316, interconnectingthrough holes 302 and solder balls 303 can be realized like in the ninthembodiment.

INDUSTRIAL APPLICABILITY

The present invention provides a printed wiring board and a method formanufacturing the same which improves electrical properties ofmultilayer printed wiring boards. Particularly, the present invention iscapable of:

(1) building up an odd number of conductive layers efficiently with nowarping;

(2) controlling interlayer delamination;

(3) forming interconnecting through holes at accurate positions; and

(4) transferring a large amount of electrical information in and out ofthe printed wiring board through the solder balls for externalconnection and achieving high densification of surface packaging.

1. A printed wiring board comprising n conductive layers and n insulating layers, wherein said n conductive layers and said n insulating layers are interleaved wherein the conductive layers are electrically connected to one another via first and second through holes, wherein n is an odd number; wherein a first of said conductive layers is a layer on which an electronic component is to be mounted with leads for electric currents in and out of the electronic component; an n-th one of said conductive layers is an external connecting layer for connecting external connecting terminals which conduct electric currents in and out of the printed wiring board; a second to an (n−1)-th ones of said conductive layers are current transmitting layers for transmitting internal currents of the printed wiring board; each of a first to an (n−1)-th ones of said insulating layers, except for the (n+1)/2-th insulating layer, has at least one of the first through holes with a plating film formed on a wall thereof to connect the conductive layers; and a surface of the n-th conductive layer is covered with an n-th and outermost one of the insulating layers wherein a central ((n+1)/2-th) insulating layer has the second through holes, each of the second through holes having a plating film formed on a wall thereof, said plating film extending to the ones of the conductive layers adjacent the central insulating layer and connecting to a first through hole, whereby warping is prevented from occurring in the printed wiring board.
 2. The printing wiring board according to claim 1, wherein the external connecting terminals are solder balls.
 3. The printed wiring board according to claim 1, wherein each of the insulating layers is formed of one of epoxy resins, phenol resins, polyimide resins, polybutadiene resins, and fluororesins.
 4. A method of manufacturing a printed wiring board having an odd number n of conductive layers interleaved with n insulating layers and are electrically connected to one another by first, second, and third interconnecting through holes, wherein a central ((n+1)/2-th) insulating layer has the second through holes, and each of the second through holes has a plating film formed on a wall thereof, said plating film extending to the ones of the conductive layers adjacent the central insulating layer, the method comprising the steps of: interposing the insulating layers between a second to an n-th conductive layer and forming the first interconnecting through holes for electrically connecting the conductive layers to one another; laminating a first prepreg and a copper foil on a surface of the second conductive layer, laminating a second prepreg on a surface of the n-th conductive layer, and simultaneously press-bonding the first and second prepregs, the copper foil, the second to n-th conductive layers, and the insulating layers to form a multilayer substrate having n insulating layers, wherein the second to n-th conductive layers are internal layers of the multilayer substrate; etching the copper foil to form a first conductive layer; forming the third interconnecting through holes in a first insulating layer and forming connecting holes in an n-th insulating layer respectively; forming a metal plating film on the walls of the third interconnecting through holes of the first insulating layer for electrically connecting the first conductive layer with a second conductive layer and connecting external connecting terminals to a surface of the n-th conductive layer exposed through the first connecting through holes of the n-th insulating layer.
 5. The method according to claim 4, wherein each of the insulating layers is formed of one of epoxy resins, phenol resins, polyimide resins, polybutadiene resins, and fluororesins.
 6. A printed wiring board comprising: an insulating substrate having at least one interconnecting through hole penetrating the insulating substrate and having a first opening and a second opening; an annular pad disposed along a peripheral edge of the first opening of the interconnecting through hole so as not to cover the first opening; a covering pad covering the second opening of the interconnecting through hole; a conductor circuit connecting an electronic component with the covering pad; a metal plating film electrically connecting the annular pad and the covering pad, the metal plating film covering a wall of the interconnecting through hole and the bottom of the interconnecting through hole defined by the covering pad such that the metal plating film has a flat surface at the wall and the bottom of the interconnecting through hole; and a solder ball for external connection bonded to the annular pad at a position offset from the interconnecting through hole.
 7. The printed wiring board according to claim 6, wherein the surface of the insulating substrate is covered with a solder resist.
 8. The printed wiring board according to claim 6, wherein the solder ball is located in alignment with the interconnecting through hole.
 9. The printed wiring board according to claim 6, wherein the solder ball is located at a position offset from the interconnecting through hole. 